It is a standard procedure in dental practice, when necessary to replace defective teeth in the oral cavity of a patient, to first make a cast impression of these teeth. A technician can from these impressions determine the three-dimensional parameters of a denture to replace the teeth.
It is known in order to avoid the need to make cast impressions to directly measure the teeth optically to obtain data for the computer-assisted design (CAD) or computer-assisted manufacture (CAM) of the replacement. In a typical instrument for this purpose, there is provided an optical probe projecting a light beam towards the surfaces of the teeth to be imaged.
The concern of the present invention is with those imaging instruments for direct optical measurement of a set of teeth which includes a probe to be inserted in the oral cavity to project a light beam toward the surfaces of the teeth and to receive light reflected therefrom which is then processed to obtain the digital data for determining the three-dimensional topology of the teeth.
One such instrument for obtaining the three-dimensional parameters of teeth in order to replace the teeth being imaged is disclosed in U.S. Pat. No. 4,575,805. In the patent, the probe takes the form of a scan bead which projects a scanning light beam toward the teeth surfaces.
Also disclosing an imaging instrument for the three-dimensional survey of teeth to obtain digital constructional data for the computer-controlled manufacture of a tooth replacement is U.S. Pat. No. 5,381,236. Another such instrument is an intra oral scanner disclosed in U.S. Pat. No. 6,359,680.
Of particular prior art interest is the imaging instrument disclosed in the PCT publication WO 00/08415 published 17 Feb. 2000 entitled “Imaging A Three-Dimensional Structure by Confocal Focusing an Array of Light Beams”. This instrument is provided with a probe in the form of an endoscope which projects light beams toward the surfaces of the teeth to be imaged and receives light reflected therefrom which is processed to obtain the required digital data.
The problem of viewability encountered when using a dental imaging instrument whose probe projects a light beam to illuminate the surfaces of the teeth to be imaged is comparable to that experienced by eyes viewing these surfaces. If the eyes are heavily coated with a tear film, the resultant image will be blurred.
In the case of surfaces of teeth in an oral cavity containing mucous, saliva, and, in some instances, blood resulting from a dental procedure, the surfaces of the teeth are usually then coated with a liquid film composed of these constituents. This liquid film which impairs the ability of an imaging instrument to clearly view the teeth surfaces, cannot easily be dislodged, for the film is ionically attracted to the teeth surfaces and has a surface tension to protect the integrity of the film and resists its evaporation.
Under ideal circumstances, the surfaces of the teeth to be imaged should be free of liquid and perfectly clean and dry to obtain an optimal degree of reflectivity and image clarity. But this can only happen when the surface reflectivity exhibits a Lambert unit of luminescence. A Lambert unit is defined as the brightness of a perfect diffusing surface that radiates or reflects one lumen per square centimeter.
A saliva-mucous liquid film coating the teeth surfaces to be illuminated does not act as a perfect diffusing surface and therefore does not exhibit optimal reflectivity. And because this film adheres ionically to the tooth surfaces, it cannot just be washed away.
In common use by dentists is an air suction pipe (negative pressure) to suck out from the oral cavity saliva and mucous which interfere with the dental procedure then in progress. Also in common use is a pressured air pipe (positive pressure) which serves to blow away debris from the region in the oral cavity is working. These pipes must be manipulated by the dentist or his assistant so that the air stream (negative or positive) can be directed to the region of interest.